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Abstract:

The present invention relates to a method for removing isocyanate from a
reaction product of isocyanate with compounds reactive towards
isocyanates, the reaction product being applied to the surface of a
rotating body A, the reaction product flowing over the surface of the
rotating body A to an outer region of the surface of the rotating body A
and isocyanate which was used for the preparation of the reaction product
and has not reacted evaporating from the mixture in the process.

Claims:

1. Method for removing isocyanate from a reaction product of isocyanate
with compounds reactive towards isocyanates, wherein the reaction product
is applied to the surface of a rotating body A, the reaction product
flowing over the surface of the rotating body A to an outer region of the
surface of the rotating body A and isocyanate which was used for the
preparation of the reaction product and has not reacted evaporating from
the mixture in the process.

2. Method according to claim 1, wherein the rotating body A is present as
a rotating disc, to the surface of which the reaction product is applied.

3. Method according to claim 1, wherein the removal of the isocyanate is
carried out by means of an apparatus which has α) a body A rotating
about an axis of rotation and β) a metering system.

4. Method according to claim 1, wherein the reaction product is present
on the surface of a rotating body A in the form of a film which has an
average thickness between 0.1 μm and 6.0 mm.

5. Method according to claim 1, wherein the average residence time of the
ingredients of the reaction product on the surface of the rotating body
is between 0.01 and 60 seconds.

6. Method according to claim 1, wherein the temperature of the rotating
body is between 70 and 300.degree. C.

7. Method according to claim 1, wherein the pressure at which the
isocyanate is removed is between 0.001 mbar and 1100 mbar.

8. Method according to claim 1, wherein the evaporated isocyanate
condenses on a body having a temperature between -196.degree. C. and
120.degree. C.

9. Method according to claim 1, wherein the content of isocyanate is
between 0.01 and 95% by weight, based on the total weight of the reaction
product, directly before the application of the substrate to the surface
of the rotating body A.

10. Method according to claim 1, wherein the content of isocyanate in the
reaction product is between 0.001 and 10% by weight, based on the total
weight of the reaction product, after the evaporation of the isocyanate
on the surface of a rotating body A.

14. Method according to claim 1, wherein a reaction product is used which
was prepared by reacting isocyanate with compounds reactive towards
isocyanates in a reactor which has α) a hot body B rotating about
an axis of rotation, β) a metering system and γ) a quench
device, a) the isocyanate and the compounds reactive towards isocyanates
being applied individually and/or as a mixture, optionally with further
components, with the aid of the metering system to the surface of the
rotating body B so that a film containing compounds reactive towards
isocyanates and isocyanate flows over the surface of the rotating body B
to an outer region of the hot surface of the rotating body B, b) the film
leaving the surface as a reaction product containing polyurethane and/or
polyurea and c) the reaction product being cooled abruptly by means of
the quench device after leaving the hot surface, the temperature of the
surface of the rotating body B being between 70 and 300.degree. C. and
the abrupt cooling of the reaction composition product effected by means
of the quench device being at least 30.degree. C.

Description:

[0001] The present invention relates to a method for removing isocyanate
from a reaction product of isocyanate with compounds reactive towards
isocyanates.

[0002] Isocyanates are valuable raw materials and are used, for example,
for the preparation of polyurethanes and polyureas. For this purpose, the
isocyanates are reacted with polyalcohols and polyamines, respectively.
The products obtained play an important role, for example, in the
industrial production of chemicals, adhesives, plastics and paints. Owing
to the molar mass distribution formed in the production, however, the
reaction products frequently still contain amounts of unreacted monomeric
isocyanates or low molecular weight reaction products which have
isocyanate groups. These may escape in gaseous form from the reaction
products and, being irritant, sensitive or toxic substances, constitute a
health hazard for the processor and end customers. Furthermore, the
monomeric isocyanates or low molecular weight reaction products remaining
in the product may disadvantageously affect the product properties.

[0003] A known method for removing monomeric diisocyanate and low
molecular weight reaction products from reaction mixtures is
distillation. Thus, for example, EP 105242A2 discloses reduction of the
remaining monomer content of a reaction product of isocyanate by
distillation with the aid of a thin-film evaporator, the reaction product
first being diluted with an inert solvent. However, this has the
disadvantage that at least a part of the inert solvent remains in the
product and can lead to problems in the following applications. In the
case of product changes, complicated cleaning of the apparatus is also
necessary. Furthermore, this method according to the prior art employs
complicated apparatus and is therefore expensive.

[0004] It was therefore an object of the present invention to provide an
economical method for removing isocyanate from a reaction product of
isocyanate with compounds reactive towards isocyanates, which method is
flexible in terms of the process. The method should be capable of being
carried out in a simple manner and should ensure a good and reproducible
product quality. Furthermore, highly viscous reaction products should
also be capable of being purified without the addition of an inert
solvent.

[0005] This object is achieved by a method for removing isocyanate from a
reaction product of isocyanate with compounds reactive towards
isocyanates, the reaction product being applied to the surface of a
rotating body A, the reaction product flowing over the surface of the
rotating body A to an outer region of the surface of the rotating body A
and isocyanate which was used for the preparation of the reaction product
and has not reacted evaporating from the mixture in the process.

[0006] The rotating body A may be disc-shaped, vase-shaped, annular or
conical, a horizontal rotating disc or a rotating disc deviating from the
horizontal by up to 45° being regarded as being preferred.
Usually, the body A has a diameter of 0.10 m to 3.0 m, preferably 0.20 m
to 2.0 m and particularly preferably of 0.20 m to 1.0 m. The surface may
be smooth or may have, for example, ripple-like or spiral mouldings which
influence the residence time of the reaction mixture. Expediently, the
body A is installed in a container which is resistant with regard to the
conditions of the method according to the invention.

[0007] The rotational velocity of the body A and the metering rate of the
reaction product are variable. Usually, the rate of revolution in
revolutions per minute is 1 to 20 000, preferably 100 to 5000 and
particularly preferably 500 to 3000. The volume of the reaction product
which is present per unit area of the hot surface on the rotating body A
is typically 0.03 to 40 ml/dm2, preferably 0.1 to 10 ml/dm2,
particularly preferably 1.0 to 5.0 ml/dm2. The average residence
time (frequency mean of the residence time spectrum) of the mixture is,
inter alia, dependent on the size of the surface, on the type of reaction
product and on the isocyanate present, on the temperature of the surface
and on the rate of revolution of the rotating body A and is usually
between 0.01 and 60 seconds, particularly preferably between 0.1 and 10
seconds, in particular 1 to 7 seconds, and is thus to be regarded as
being extremely short. This ensures that the extent of possible
decomposition reactions and the formation of undesired products are
greatly reduced and hence the quality of the substrates is maintained.

[0008] In a preferred embodiment of the invention, the removal of the
isocyanate is carried out by means of an apparatus which has [0009]
α) a body A rotating about a preferably centrally arranged axis of
rotation and [0010] β) a metering system.

[0011] In a further embodiment, the apparatus may have a quench device.
The quench device is preferably present as at least one cooling wall
which surrounds the rotating disc and which the reaction product strikes
after leaving the surface. In this embodiment, the method according to
the invention ensures that the reaction product from which the isocyanate
is to be removed can be strongly heated by the body A in a very short
time, thermally promoted, undesired secondary reactions being prevented
by the subsequent quenching. The abrupt cooling by means of the quench
device is effected within at most five seconds, preferably within only
one second.

[0012] For effective removal of the isocyanate, it may also be expedient
to pass the reaction product several times over the surface of the
rotating body A. In a further embodiment of the invention, the surface
extends to further rotating bodies so that the reaction product passes
from the surface of the rotating body A to the surface of at least one
further rotating body. The further rotating bodies are expediently
constituted to correspond to the body A. Typically, body A then feeds the
further bodies with the reaction product. The reaction product leaves
this at least one further body and, if required, can then be abruptly
cooled by means of the quench device.

[0013] It is to be regarded as being preferred that the reaction product
is present on the surface of the rotating body A in the form of a film
which has an average thickness between 0.1 μm and 6.0 mm, preferably
between 60 and 1000 μm, particularly preferably between 100 and 500
μm.

[0014] The method according to the invention can be carried out at
atmospheric pressure or slightly superatmospheric pressure and also in an
atmosphere of dry inert gas. However, it may also be expedient to
generate a vacuum, in general pressures between 0.001 mbar and 1100 mbar,
particularly preferably between 0.01 mbar and 40 mbar, in particular
between 0.02 mbar and 20 mbar, having proved to be advantageous. A
preferred embodiment of the present invention furthermore envisages that
the evaporated isocyanate will be expelled with a gas or dry air, in
particular inert gas. It is furthermore to be regarded as being preferred
that at the same time a vacuum is applied and the evaporated isocyanate
is expelled with a gas or dry air, in particular inert gas.

[0015] The temperature of the rotating body A, in particular of the
surface facing the mixture, may be varied in wide regions and depends
both on the reaction products used, the isocyanate and the residence time
on the body A and on the pressure. Temperatures between 70 and
300° C., particularly preferably between 25 and 270° C., in
particular between 150 and 250° C. have proved to be expedient.
The rotating body A and/or the reaction product can be heated, for
example electrically, with a heat-transfer liquid, with vapour, with a
laser, with microwave radiation or by means of infrared radiation.

[0016] It has furthermore proved to be expedient to condense the
evaporated isocyanate on a body having a temperature between -196°
C. and 120° C., particularly preferably between -78 and 20°
C., in particular between -78 and 0° C. In this context, a
preferred embodiment envisages surrounding the rotating body A with at
least one surface on which isocyanate can condense, it being preferred
that the surface has an inclination so that the condensed isocyanate is
removed from the rotating body A by gravitation along the surface.

[0017] However, it may also be expedient to heat the surfaces surrounding
the body A in order to prevent condensation of isocyanate. In this
embodiment, the evaporated isocyanate can be removed by a vacuum or an
inert gas stream.

[0018] The isocyanate content of the reaction products used is not
critical. In particular, the method according to the invention is
suitable if the isocyanate content of the reaction products used is
between 0.01 and 95% by weight, particularly preferably between 0.1 and
75% by weight, in particular between 0.2 and 67% by weight, based on the
total weight of the reaction product, directly before the application to
the surface of the rotating body A. Here, it is to be regarded as being
preferred that the isocyanate content in the mixture after removal of the
isocyanate by evaporation on the surface of the rotating body A is
between 0.001 and 10% by weight, particularly preferably between 0.02 and
5% by weight, in particular between 0.05 and 2% by weight, based on the
total weight of the reaction product.

[0021] The compounds reactive towards isocyanates are preferably compounds
having hydroxyl groups and/or amino groups. Polyetherpolyols,
polyesterpolyols, polybutadienepolyols and polycarbonatepolyols are
particularly preferred. The polyols and/or polyamines preferably contain
between two and 10, particularly preferably between two and three,
hydroxyl groups and/or amino groups and have a weight average molecular
weight between 32 and 20 000, particularly preferably between 90 and 18
000 g/mol. Suitable as polyols are preferably the polyhydroxy compounds
which are liquid, glassy solid/amorphous or crystalline at room
temperature. Difunctional polypropylene glycols may be mentioned as
typical examples. It is also possible to use random copolymers and/or
block copolymers of ethylene oxide and propylene oxide which have
hydroxyl groups. Suitable polyetherpolyols are the polyethers known per
se in polyurethane chemistry, such as the polyols prepared using
initiator molecules from styrene oxide, propylene oxide, butylene oxide,
tetrahydrofuran or epichlorohydrin. In particular,
poly(oxytetramethylene) glycol (poly-THF), 1,2-polybutylene glycol or
mixtures thereof are specifically suitable. In particular, polypropylene
oxide and polyethylene oxide and mixtures thereof are suitable. A further
copolymer type which can be used as the polyol component and has terminal
hydroxyl groups is according to the general formula (preparable, for
example, by means of "controlled" high-speed anionic polymerization
according to Macromolecules 2004, 37, 4038-4043):

##STR00001##

in which R is identical or different and is preferably represented by
OMe, OiPr, Cl or Br.

[0023] A further suitable group of polyols comprises the polyesters, for
example based on caprolactone, which are also referred to as
"polycaprolactones". Further polyols which may be used are
polycarbonate-polyols and dimeric diols and polyols based on vegetable
oils and their derivatives, such as castor oil and derivatives thereof,
or epoxidized soybean oil. Also suitable are polycarbonates which have
hydroxyl groups and are obtainable by reaction of carbonic acid
derivatives, e.g. diphenyl carbonate, dimethyl carbonate or phosgene,
with diols. Ethylene glycol, 1,2- and 1,3-propanediol, 1,3- and
1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, neopentylglycol,
1,4-bishydroxymethylcyclohexane, 2-methyl-1,3-propanediol,
2,2,4-trimethylpentane-1,3-diol, dipropylene glycol, polypropylene
glycols, dibutylene glycol, polybutylene glycols, bisphenol A,
tetrabromobisphenol A, glycerol, trimethylolpropane, hexane-1,2,6-triol,
butane-1,2,4-triol, trimethylolpropane, pentaerythritol, chinitol,
mannitol, sorbitol, methylglycoside and 1,3,4,6-dianhydrohexite are
specifically suitable. The hydroxyl-functional polybutadienes, which are
commercially available, inter alia, under the trade name "Poly-bd®",
can also be used as polyols, as can the hydrogenated analogues thereof.
Furthermore, hydroxy-functional polysulphides, which are marketed, for
example, under the trade name "Thiokol® NPS-282", and
hydroxy-functional polysiloxanes are suitable.

[0024] In particular, hydrazine, hydrazine hydrate and substituted
hydrazines, such as N-methylhydrazine, N,N'-dimethylhydrazine, acid
dihydrazides, adipic acid, methyl-adipic acid, sebacic acid, hydracrylic
acid, terephthalic acid, semicarbazidoalkylene hydrazides, such as
13-semicarbazidopropionic acid hydrazide, semicarbazidoalkylene carbazine
esters, such as, for example, 2-semicarbazidoethyl carbazine ester,
and/or aminosemicarbazide compounds, such as
13-aminoethylsemicarbazidocarbonate, are suitable as polyamines which can
be used according to the invention.

[0025] Polyamines, for example those which are marketed under the trade
name Jeffamine® (these are polyetherpolyamines) are also suitable.

[0026] Suitable polyols and/or polyamines are also the species known as
so-called chain extenders, which react with excess isocyanate groups in
the preparation of polyurethanes and polyureas, usually have a molecular
weight of less than 400 and are frequently present in the form of
polyols, aminopolyols or aliphatic, cycloaliphatic or araliphatic
polyamines.

[0032] Finally, it should be mentioned that the polyols and/or polyamines
may contain double bonds which may result, for example, from long-chain,
aliphatic carboxylic acids or fatty alcohols. Functionalization with
olefinic double bonds is also possible, for example, by the incorporation
of vinylic or allylic groups. These may originate, for example, from
unsaturated acids, such as maleic anhydride, acrylic acid or methacrylic
acid and the respective esters thereof.

[0034] In this context, it has proved particularly surprising that the
method according to the invention is also suitable in an outstanding
manner for removing isocyanate from highly viscous liquids, it being
possible to remove even very small amounts of isocyanate effectively. In
addition to the viscosity, the chemical properties of the reaction
products used also play an important role. The method according to the
present invention gives outstanding results both for polyurethanes and
for polyureas and for oligomeric isocyanate mixtures. Furthermore, the
method according to the invention can be carried out with uncomplicated
apparatus, relatively high substance throughputs being possible. Thus,
the claimed method provides a very economical alternative to the methods
already known, even for the industrial purification of reaction products
of isocyanate.

[0035] A particular embodiment of the present invention envisages using a
reaction product which was prepared by reacting isocyanate with compounds
reactive towards isocyanates in a reactor which has [0036] α) a
hot body B rotating about a preferably centrally arranged axis of
rotation, [0037] β) a metering system and [0038] γ) a quench
device, [0039] a) the isocyanate and the compounds reactive towards
isocyanates being applied individually and/or as a mixture, optionally
with further components, with the aid of the metering system to the
surface of the rotating body B so that a film containing compounds
reactive towards isocyanates and isocyanate flows over the surface of the
rotating body B to an outer region of the hot surface of the rotating
body B, [0040] b) the film leaving the surface as a reaction product
containing polyurethane and/or polyurea and [0041] c) the reaction
composition being cooled abruptly by means of the quench device after
leaving the hot surface, the temperature of the surface of the rotating
body B being between 70 and 300° C., particularly preferably
between 160 and 250° C., and the abrupt cooling of the reaction
composition effected by means of the quench device being at least
30° C.

[0042] The quench device is in general preferably present in the form of
one or more cooling walls which permit the abrupt cooling of the reaction
mixture. The cooling walls, which are frequently cylindrical or conical,
have either a smooth or a rough surface, the temperature of which is
typically between -50° C. and 200° C. The abrupt cooling of
the reaction composition effected by means of the quench device is
preferably at least 50° C., preferably at least 100° C.

[0043] Here, the hot rotating body B is expediently constituted to
correspond to the body A. Particularly advantageous here is that both the
preparation of the reaction product of isocyanate with compounds reactive
towards isocyanates and the removal of the isocyanate from the reaction
product can be carried out with the same apparatus.

[0044] The molar ratio of the isocyanate groups of the isocyanate
component used to the sum of the amino groups and/or hydroxyl groups of
the polyols and/or polyamines used is preferably between 0.1 and 20,
particularly preferably between 1.3 and 10, in particular between 1.8 and
5.

[0045] Advantageously, a catalyst suitable for the preparation of
polyurethanes or polyureas is used as a component of the starting
reaction mixture in the method according to the invention. Suitable
catalysts are the customary catalysts of polyurethane chemistry which are
known per se, such as acids, e.g. para-toluenesulphonic acid, or tertiary
amines, such as, for example, triethylamine, triethylenediamine (DABCO)
or those which have atoms such as, for example, Sn, Mn, Fe, Co, Cd, Ni,
Cu, Zn, Zr, Ti, Hf, Al, Th, Ce, Bi, Hg, N or P. The molar ratio of
catalyst to isocyanate is dependent on the type of isocyanate and on the
type of catalyst and is usually between 0 and 0.1, preferably 0 to 0.03.

[0046] The temperature of the hot body B and the contact time on this body
are preferably established so that between 5 and 99.99% by weight of the
maximum amount of isocyanate groups which can be reacted with the amount
of polyol and optionally amine used have preferably reacted with hydroxyl
and optionally amino groups of the polyol and optionally amine.